Add roundtrip

Author: lorenzwalthert

R/transform-files.R

@@ -94,20 +94,20 @@ parse_transform_serialize <- function(text, transformers) {
     return("")
   }
   transformed_pd <- apply_transformers(pd_nested, transformers)
-  # TODO verify_roundtrip
   flattened_pd <- post_visit(transformed_pd, list(extract_terminals)) %>%
     enrich_terminals(transformers$use_raw_indention) %>%
     apply_ref_indention() %>%
     set_regex_indention(
       pattern          = transformers$reindention$regex_pattern,
       target_indention = transformers$reindention$indention,
-      comments_only    = transformers$reindention$comments_only)
-
+      comments_only    = transformers$reindention$comments_only
+  )
   serialized_transformed_text <-
     serialize_parse_data_flattened(flattened_pd, start_line = start_line)
+  verify_roundtrip(text, serialized_transformed_text, transformers)
   serialized_transformed_text
-}
 
+}
 
 #' Apply transformers to a parse table
 #'
@@ -154,5 +154,43 @@ apply_transformers <- function(pd_nested, transformers) {
     outer_indention_refs = NA
   )
   transformed_absolute_indent
+}
 
+
+#' Verify the styling if possible
+#'
+#' If scope was set to "line_breaks" or lower (compare [tidyverse_style()]),
+#' we can compare the expression before and after styling and return an error if
+#' it is not the same. Note that this method ignores comments and no
+#' verification can be conducted if scope > "line_breaks".
+#' @param old_text The initial expression in its character representation.
+#' @param new_text The styled expression in its character representation.
+#' @param transformers The list of transformer functions used for styling.
+#'   Needed for reverse engineering the scope.
+#' @examples
+#' styler:::verify_roundtrip("a+1", "a + 1", tidyverse_style(scope = "line_breaks"))
+#' styler:::verify_roundtrip(
+#'   "a+1",
+#'   "a + 1 # comments are dropped",
+#'   tidyverse_style(scope = "line_breaks")
+#' )
+#' \dontrun{
+#' styler:::verify_roundtrip("a+1", "b - 3", tidyverse_style(scope = "line_breaks"))
+#' }
+verify_roundtrip <- function(old_text, new_text, transformers) {
+  if (is.null(transformers$token)) {
+    expressions_are_identical <- identical(
+      parse(text = old_text, keep.source = FALSE),
+      parse(text = new_text, keep.source = FALSE)
+    )
+    if (!expressions_are_identical) {
+      msg <- paste(
+        "The expression evaluated before the styling is not the same as the",
+        "expression after styling. This should not happen. Please file a",
+        "bug report on GitHub (https://github.com/r-lib/styler/issues)",
+        "using a reprex."
+      )
+      stop(msg, call. = FALSE)
+    }
+  }
 }

man/verify_roundtrip.Rd

@@ -0,0 +1,25 @@
+context("roundtrip works")
+
+test_that("correct styling does not give an error for scope < tokens", {
+  expect_error(verify_roundtrip(
+    "1+1", "1 + 1", tidyverse_style(scope = "spaces")
+  ), NA)
+  expect_error(verify_roundtrip(
+    "1+1", "1 + 1", tidyverse_style(scope = "line_breaks")
+  ), NA)
+  expect_error(verify_roundtrip(
+    "1+1", "10+10", tidyverse_style(scope = "tokens")
+  ), NA)
+})
+
+test_that("incorrect styling does give an error", {
+  expect_error(verify_roundtrip(
+    "1-1", "1 + 1", tidyverse_style(scope = "spaces")
+  ), "bug")
+  expect_error(verify_roundtrip(
+    "1-1", "1 + 1", tidyverse_style(scope = "line_breaks")
+  ), "bug")
+  expect_error(verify_roundtrip(
+    "1-1", "1 + 1", tidyverse_style(scope = "tokens")
+  ), NA)
+})